ribosome

Examples of ribosome in the following topics:

• Ribosomes

  • Ribosomes are not membrane bound.
  • All prokaryotes have 70S (where S=Svedberg units) ribosomes while eukaryotes contain larger 80S ribosomes in their cytosol.
  • The 70S ribosome is made up of a 50S and 30S subunits.
  • Ribosome assembly consists of transcription, translation, the folding of rRNA and ribosomal proteins, the binding of ribosomal proteins, and the binding and release of the assembly components to make the ribosome.
  • The ribosome assembles amino acids into a protein.

• Unsticking Stuck Ribosomes

  • Ribosomes can get stuck on mRNAs, cells have ways of unsticking them.
  • As mRNAs are transcribed a phenomenon of "stuck" or stalled ribosomes can occur.
  • The first pathway proteins bind to the stuck ribosome.
  • This binding allows the ribosome to eject the stuck mRNA molecule – this even frees the ribosome and allows it to translate other transcripts.
  • It is generally agreed that tmRNA first occupies the empty A site of the stalled ribosome.

• Inhibiting Protein Synthesis

  • It usually refers to substances, such as antimicrobial drugs, that act at the ribosome level.
  • The differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected.
  • The ribosome has three sites: the A site, the P site, and the E site (not shown in ).
  • The P site is where the peptidyl tRNA is formed in the ribosome.
  • Diagram showing how the translation of the mRNA and the synthesis of proteins is made by ribosomes.

• Naturally Occurring Antimicrobial Drugs: Antibiotics

  • While a broad interpretation of this definition could be used to describe nearly any antibiotic, in practice, it usually refers to substances that act at the ribosome level (either the ribosome itself or the translation factor), taking advantage of the major differences between prokaryotic and eukaryotic ribosome structures.
  • Macrolides (as well as inhibiting ribosomal translocation and other potential mechanisms) bind to the 50s ribosomal subunits, inhibiting peptidyl transfer.
  • Quinupristin binds to a nearby site on the 50S ribosomal subunit and prevents elongation of the polypeptide.
  • Fusidic acid prevents the turnover of elongation factor G (EF-G) from the ribosome.
  • Therefore, it binds to the ribosomal A site and participates in peptide bond formation, producing peptidyl-puromycin.

• Nucleic Acid Sequencing and rRNA Analysis

  • Sixteen S ribosomal RNA (or 16S rRNA) is a component of the 30S small subunit of prokaryotic ribosomes .
  • Structure and shape of the E.coli 70S ribosome.
  • The large 50S ribosomal subunit (red) and small 30S ribosomal subunit (blue) are shown with a 200 Ångstrom (20 nm) scale bar.
  • For the 50S subunit, the 23S (dark red) and 5S (orange red) rRNAs and the ribosomal proteins (pink) are shown.
  • For the 30S subunit, the 16S rRNA (dark blue) and the ribosomal proteins (light blue) are shown.

• Attenuation

  • The stop signal, referred to as the attenuator, prevents the proper function of the ribosomal complex, stopping the process.
  • In times of need, the attenuator within the mRNA sequence will be bypassed by the ribosome and proper translation will occur.
  • The Shine-Dalgarno sequence is a bacterial specific sequence that indicates the site for ribosomal binding to allow for proper translation to occur.
  • The formation of this hairpin-loop structure results in the inability of the ribosomal complexes to form and proceed with proper translation.

• Chemical Analysis of Microbial Cytoplasm

  • Macromolecules found within bacterial cytoplasm include the nucleoid region, ribosomes, proteins, and enzymes.
  • The ribosomes, similar to ribosomes in eukaryotes, are responsible for protein synthesis.
  • Unlike eukaryotes, prokaryotes, specifically bacteria, typically contain one cytosol-specific ribosome.
  • Eukaryotes have multiple types of ribosomes, including the mitochondria and cytosol).

• Regulation by Biosynthetic Enzymes

  • During attenuation, the ribosome becomes stalled (delayed) in the attenuator region in the mRNA leader.
  • There are now many equivalent examples where the translation, not transcription, is terminated by sequestering the Shine-Dalgarno sequence (ribosomal binding site) in a hairpin-loop structure.
  • When the RNA polymerase binds and transcribes the trp gene, the ribosome will start translating.
  • A high level of tryptophan will permit ribosomes to translate the attenuator sequence domains 1 and 2, allowing domains 3 and 4 to form a hairpin structure, which results in termination of transcription of the trp operon.
  • In contrast, a low level of tryptophan means that the ribosome will stall at domain 1, causing the domains 2 and 3 to form a different hairpin structure that does not signal termination of transcription.

• Nonribosomal Peptide Antibiotics

  • While there exists a wide range of peptides that are not synthesized by ribosomes, the term nonribosomal peptide typically refers to a very specific set of these as discussed in this article.
  • Nonribosomal peptides are synthesized by nonribosomal peptide synthetases, which, unlike the ribosomes, are independent of messenger RNA.

• Control of Transcription in Archaea

  • Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria, with the archaean RNA polymerase and ribosomes being very close to their equivalents in eukaryotes.
  • Post-transcriptional modification is simpler than in eukaryotes, since most archaean genes lack introns, although there are many introns in their transfer RNA and ribosomal RNA genes, and introns may occur in a few protein-encoding genes.